Method for preparing soluble polyamideimides

ABSTRACT

PHENOLIC ACIDIC SOLVENT-SOLUBLE AND INFUSIBLE LINEAR AROMATIC POLYAMIDE-IMIDES OF HIGH MOLECULAR WEIGHT HAVING AMIDE BONDING AND A 5-MEMBERED IMIDE RING IN THE MOLECULE WHICH IS OBTAINED BY SUBJECTING TRICARBOXYLIC ANHYDRIDE AND DIISOCYANATE TO HEATING AND MELT STATE REACTION AT A TEMPERATURE NOT EXCEEDING 205*C, AND THEN SUBJECTING THEN TO SOLID STATE POLYMERIZATION REACTION AT A TEMPERATUE NOT EXCEEDING 205*C, THE MOLAR  RATIO BETWEEN SAID DIISOCYANATE AND SAID TRICARBOXYLIC ANHYDRIDE BEING 1:1.

United States Patent ()flice 3,803,100 Patented Apr. 9, 1974 US. Cl.26078 TF 6 Claims ABSTRACT OF THE DISCLOSURE Phenolic acidicsolvent-soluble and infusible linear aromatic polyamide-imides of highmolecular weight having amide bonding and a S-membered imide ring in themolecule which is obtained by subjecting tricarboxylic anhydride anddiisocyanate to heating and melt state reaction at a temperature notexceeding 205 C., and then subjecting them to solid state polymerizationreaction at a temperature not exceeding 205 C., the molar ratio betweensaid 'diisocyanate and said tricarboxylic anhydride being 1:1.

CROSS REFERENCE TO RELATED APPLICATIONS This application is acontinuation-in-part application of S'er. No. 693,747, filed on Dec. 27,1967, now abandoned and claims priority based upon Japanese applicationsfiled Dec. 29, 1966.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to phenolic acidic solvent-soluble and infusible linear aromaticpolyamide-imides of high molecular weight obtained by heatingtricarboxylic anhydrides and diisocyanates for melt phase reaction andthen causing them to undergo solid state reaction, and to their polymersolutions, and to a method of manufacutring them.

More particularly, this invention relates to phenolic acidicsolvent-soluble and infusible linear aromatic polyamide imides of highmolecular weight having amide bond and five-membered imide ring in themolecule obtained by heating tricarboxylic anhydrides and diisocyanatesfor melt phase reaction, converting them into an infusible porous solidas the reaction goes on, and causing the low molecular weight polymer,still containing a great deal of isocyanate groups, acid anhydridegroups and carboxyl groups remaining in it, to undergo solid statereaction in continuation under fully controlled temperature conditions(205 C. or less). The invention also relates to stable polymer solutionsobtainable by dissolving the product in a solvent, and to a method ofmanufacturing the resins.

Description of the prior art It has long been known that generally anisocyanate group reacts with a carboxyl group and forms an amide bond,generating carbon dioxide. It has also been known that an isocyanategroup reacts with an acid anhydride group and forms a five-memberedimide ring, generating carbon dioxide. It is also publicly known thatcellular plas tic products of insoluble and infusible foamed productsobtained by using carbon dioxide generated when tricarboxylicanhydrides, containing a carboxyl group and an acid anhydride group, arecaused to react with polyisocyanates. It is also publicly known that ifdiisocyanates and tetracarboxylic dianhydride are heated to react witheach other in such a basic solvent as N.N-dimethylacetamide,N.N-dimethylformamide, N-methyl-Z-pyrrolidone, etc., a reaction takesplace generating carbon dioxide. However, the product becomes insolublein the basic solvent while it still has a low molecular weight,precipitates and gets out of the reaction system, so that it becomes aheterogeneous system. Thus, no high molecular weight products areobtained.

In recent times a great deal of investigation is being made for highpolymers which have excellent thermal, mechanical, electrical, chemicaland other properties. Especially, polyimides are put to practical use inindustry. These have various excellent properties, such as thermalstability, owing to the five-membered imide ring. It is generally knownthat thermal stability is remarkably improved by the introduction of aheterocyclic ring into the molecule. However, as can be seen from theaforementioned described reaction of diisocyanates and tetracarboxylicdianhydrides, the product, having formed a heterocyclic ring, isinsoluble in the solvent. For this reason, a polymer solution ofpolyimide is obtained in the state of polyamic acid by subjectingdiamine and tetracarboxylic dianhydride to a low temperature solutionpolymerization process in a basic solvent like N.N-dimethylacetamide,N.N-dimethylformamide, N-methyl-2-pyrrolidone, etc.

Because of the above fact, a great deal of caution is required instoring the solution. In addition, it is known that the product in thestate of polyamic acid is subject to hydrolysis, and is extremelyunstable because of the remarkable moisture-absorbing property of basicsolvents. In addition, polyimides have poor abrasion resistance, so thatcautious handling will be necessary when it is used in making electricwires of the like. Also, because of the inherent property of thefivc-membered imide ring, it

has poor alkali resistance. It immersed in a 5% caustic soda solutionfor 24 hours, a polyimide film is almost all dissolved.

On the other hand, whole aromatic polyamides are synthesized fromdi-acid chloride and diamine. This whole aromatic polyamide is extremelysuperior in abrasion resistance and alkali resistance because of itsamide bond. Though it is not as good as a polyimide, its thermalstability is very good when compared with that of other generally knownpolymers. Needless to say, it is insoluble in cresols and it has adisadvantage in that it has very little solubility, or is even insolublein such basic solvents as N.N dimethylformamide, N.N dimethylacetamide,N.N-methyl-Z-pyrrolidone, etc.

Phenolic acidic solvent-soluble and infusible linear aromaticpolyamide-imides of high molecular weight synthesized according to thepresent invention possess excellent thermal stability, havingfive-membered imide ring which is the greatest characteristic feature ofthe polyimide. On the other hand, it possesses excellent abrasionresistance and alkali resistance which are the merits of whole aromaticpolyamides. Furthermore, it has an excellent solubility notwithstandingthe fact that five-mem- 3- bered imide ring has already been formed andit has aromatic amide bonding. In addition, a polymer solution of a highconcentration may be obtained, even if a, phenolic acidic solvent likecresol is employed.

In this connection, there is no fear of hydrolysis because thefive-membered imide ring has already been formed. When a phenolic acidicsolvent is used, it scarcely absorbs moisture, so that a stable polymersolution may be obtained even if it may be left in whatever condition.

The present invention makes it also possible to use as startingmaterials tricarboxylic anhydrides, dicarboxylic acids, tetracarboxyldianhydrides and diisocyanates which are easily obtainable on themarket, and to use as a sol vent, material having a phenolic hydroxygroup, like cresol which is very cheap and exhibits an excellent workingstability. The solvent is used here because the polymeric products areinfusible, so that a polymer solution is prepared due to the necessityof working. In the final stage of the application, therefore, thesolvent is heated and removed. Generally, the solid contents in apolymer solution are 40% or less at best, the balance of 60% being thesolvent. It is, therefore, obvious that it is extremely advantageous forindustrial purposes if a solvent which is cheap and of excellentworkability and stability can be used.

Phenolic acidic solvent-soluble and infusible linear aromaticpolyamide-imides of high molecular weight synthesized by the method ofthe present invention may be dissolved in a phenolic acidic solvent likecresol which reacts with the isocyanate group, carboxyl group and acidanhydride group, since its polymeric products may be obtained in a solidstate. If a phenolic acidic solvent like cresol is used, such solvent isvery cheap, has a good workability and is not moisture-absorbent, sothat the polymer solution is stable in whatever conditions it may beleft.

If the reaction of the tricarboxylic anhydride with diisocyanate isconducted in a phenolic acidic solvent such as cresol, which is reactivewith the isocyanate group, carboxyl group and acid anhydride group, thereaction between the phenolic acidic solvent and the isocyanate grouphaving been completed prior to the reaction between the tricarboxylicanhydride and the isocyanate group, inhibits the objective phenolicacidic solvent linear aromatic polyamide-imide of high molecular weight,from being produced by the reaction between the tricar-boxylic anhydrideand diisocyanate. Moreover, the reactant takes the solvent-soluble form,as set forth in Comparison Example 5. Thus, the objective material ofthe present invention cannot be obtained.

To obtain a polymer solution by using a reactive solvent like cresol isonly possible when the solid state polymerization method of thisinvention is employed.

A part of the aforementioned tricarboxylic anhydrides may be substitutedwith dicarboxylic acids or tetracarboxylic dianhydrides within the rangepermitted by solubility, depending on the properties required. In thiscase, is is preferable for the reasons of foam forming, solubility,etc., that the dicarboxylic acids are 60 mol percent or less oftricarboxylic acid anhydrides and tetracarboxylic dianhydrides are 25mol percent or less.

In the present invention, diisocyanates are used to obtain a solubleresin.

The present inventors have discovered that the high molecular weightpolymeric products obtained by the method of this invention have afilm-forming ability and are extremely useful as electrical insulatingmaterials. The film, insulated electric wire, varnish cloths, laminates,laminated tubes, etc., made from the solution of said polymer are highlyexcellent with respect to electrical properties, thermal properties,mechanical properties and chemical properties.

The object of the invention of this application is, as already stated,to obtain phenolic acidic solvent-soluble and infusible linear aromaticp yamide-imides of high molecular weight which have an amide bond and afivemembered imide ring in the molecule.

SUMMARY OF THE INVENTION It is, therefore, of importance in thisinvention that tricarboxylic anhydrides and diisocyanates are subjectedto melt phase reaction and infusible resinous products are then formed,and in order to obtain products of higher molecular weight from saidinfusible resinous products, it is necessary to effect polymerization inthe solid state under fully controlled temperature conditions. That isto say, in order to prevent the formation of an insoluble phenolicacidic solvent product, it is necessary that the temperature is 205 C.or lower when said infusible resinous products are subjected to reactionin a solid state.

The reason why the temperature at which the solid state polymerizationreaction is caused to take place is prescribed to be 205 C., or lower isbecause it is necessary to have the reaction take place selectively at atemperature which is completely controlled so that carboxylic group andanhydride group may not react togetherto make the product which isinsoluble in a phenolic acidic solvent. If the solid statepolymerization is effected at a temperature exceeding 205 C., variousside reactions take place because of the great activity of isocyanategroup. Thus, the polymeric products become crosslinked or aretransformed into insoluble phenolic acidic solvents and organic acidicsolvents. Eventually insoluble phenolic acidic solvent and organicacidic solvent products are formed which are not suitable for thepurpose of the present invention. This is shown in Comparison Example 4.

The fact that the polymeric products obtained after the solid statereaction are those of a higher degree of polymerization (the reactionhaving proceeded further than that of the products of the melt phasereaction), has been proved by means of infrared spectrum and themeasurement of reduced specific viscosity.

However, in the case where the solid reaction taking place at atemperature of above 205 C., the hydrogen atom in the formed amide bondbecomes an active hydrogen and reacts with the isocyanate group. Thecarboxyl group reacts with the isocyanate group to be decarbonated andto the group or other groups (other than the amide group). In addition,pentacyclic imide bonding is introduced into the molecular structure bya side reaction, such as polymerization of the isocyanate groups witheach other. Moreover, the reaction products of these reactions arethree-dimensionalized and insolubilized and the object of the presentinvention, i.e. to obtain a straight chain, high molecular weight,soluble polyamide having excellent heat resistance, is prevented. Suchthree-dimensionalization must be avoided in order to obtain a polymersolution and it is an indispensable requirement in the obtaining of apolymer solution to first obtain a straight chain, high molecular weightmolecule.

One of the salient features of the product applicable to the presentinvention and its process for preparation resides in the fact that thereactants employed (that is, the diisoycanate and the tricarboxylicanhydride) are present in a molar ratio of 1:1 respectively. It is thisspecific molar reactant ratio which permits the products of the presentinvention to attain the necessary degree of polymerization, whichimparts to these compounds the vario s att ib tes here o efore al udeto. It is because of these attributes, that these compounds produced inthe present invention find suitable use in the field of films andheat-insulating materials.

In addition to the foregoing requirement, two other essential featuresmust be present; that is, there must first occur, a melt state reactionfollowed by a solid state reaction, wherein the temperature range of themelt state reaction ranges from 40 C. to not exceeding 205 C., and thetemperature range of the solid state reaction is the same as that forthe melt state reaction.

Based on the foregoing, it is readily apparent that in the absence ofany one of the aforementioned three features, the goals of the presentinvention cannot be attained. For example, in the case where the molarratio between the tricarboxylic anhydride and diisocyanate fails toreach 1:1, there can only be obtained an insoluble lower molecularWeight or terpolymerized product as described in Comparison Example 1.In the case Where the temperature range fails to meet the requirementsnecessary (between 40 C. and 205 C.) again, a terpolymerized product isobtained, which is solvent-insoluble and infusible as shown byComparison Example 4. Finally, in the case where both a solid statereaction and melt state reaction have not occurred, a product is formedwhich lacks suflicient high molecular weight and which further lacks theability to act as a heat-insulating film. See for instance, ComparisonExample 5.

When tricarboxylic anhydrides and diisocyanates are caused to react witheach other, the speed of the melt reaction and solid state reaction canbe increased and products of a higher degree of polymerization can beobtained, providing an organic polar reagent is used as a catalyst.

The use of such an organic polar reagent as N.N-dimethylamide in acatalytic quantity activates the isocyanate group. As a matter of fact,in the reaction of a carboxyl group or acid anhydride group, and anisocyanate group as that of the present invention, it is obvious asshown in the embodiments that organic polar reagents have a catalyticeffect.

As already stated, it is necessary to have the solid state reaction takeplace under controlled temperature conditions in order to obtain aphenolic acidic solvent-soluble infusible linear aromatic polyamideimideof high molecular Weight. Thus, the reaction speed is slow. When saidorganic polar reagent is used in the reaction of the invention of thisapplication, it has a remarkable catalytic effect in the moltencondition at the initial stage of the reaction and in addition it isdistributed completely uniformly in the reaction product which foams andsolidifies, so that it retains its catalytic effect in the subsequentsolid state reaction as well.

These polar reagents evaporate together with the solvent when thepolymer solution is heated to remove the solvent and leave no residue atall. Besides, even if a small quantity of such reagents is present in apolymer solution, it has no detrimental effect on the stability of amidebond and five-member irnide ring. As mentioned later, the reaction maybe accelerated by the use of a catalyst.

If tricarboxylic anhydrides and diisocyanates are caused to react witheach other, carbon dioxide is generated as a result of the reaction.When the reaction products become infusible, carbon dioxide is enclosedtherein and produces foams. As is Well known, a foamed solid is highlyuseful as a heat insulating material. It is very difiicult to heat thewhole of a solid uniformly under the condition that the temperature is205 C., or lower for solid state reaction, which consequently takes along time. In the invention of the present application therefore, asolvent which does not react with the isocyanate group, acid anhydridegroup and carboxyl group and does not dissolve and swell the resinousproducts and whose boiling point does not exceed 205 C., is added whenthe solid state reaction is effected in order to heat them from theinterior,

thereby making it possible to effect uniform heating and to effect thereaction under fully controlled temperature conditions. This isremarkably efiective, in not only increasing the reaction speed, butalso enhancing the final value of reduced specific viscosity.

If tricarboxylic anhydrides containing carboxyl groups and anhydridegroups and isocyanates are caused to react with each other, 44.8 literscarbon dioxide at 0 C., l atmospheric pressure, is generated for everymol of tricarboxylic anhydride.

Because of this carbon dioxide, the reaction products foam as theybecome viscous towards the end of the molten condition, and become verybulky. It is very difficult to control their volume to a fixed volume.In addition, the reaction of isocyanate group and carboxyl group andacid anhydride group calls for a high temperature, so that it isnecessary to isolate the reaction system from the outer atmosphere inorder to avoid side reactions that may be caused by active hydrogencompounds more active than carboxyl groups and acid anhydride groups,such as water in the air. Consequently, where the object is not toobtain a foamed product but to obtain the powder of a resin obtained ora polymer solution, the fact that the product acquires a very bad foamedvolume and it is impossible to control that volume, proves to be a verydisadvantageous condition in utilizing the method for industrialpurposes. This is due to the fact that the weight of the materials whichcan be subjected to the reaction in a vessel of a fixed capacity is verylittle and the operation becomes unstable. It will have a very greatindustrial value if a method which enables the volume of the reactionproducts to decrease and which makes it possible to control it to avolume as required is obtained. Also the reaction products in the endcondition of the melt phase reaction still contain a great deal ofunreacted isocyanate groups, carboxyl groups and acid anhydride groups,and are polymers of very low molecular weight. In order to obtainphenolic acidic solvent-soluble and infusible linear aromaticpolyamide-imides of high molecular weight which has a practical value,it is necessary to effect the solid state polymerization reaction underfully controlled temperature conditions in continuation after foamingand solidifying to avoid reaction to make them insoluble.

If therefore, an organic liquid which is chemically unreactive and doesnot dissolve the reaction products is added from the initial stage ofthe reaction, the foamed volume is remarkably decreased depending on thequantity added and it becomes possible to control the volume. As is wellknown, a foamed material is usable as a heatinsulating material. Also inthe reaction of the present invention, since the thermal conduction tothe interior decreases suddenly upon foaming, so that the temperaturedistribution becomes non-uniform, it becomes impossible to have thereaction proceed uniformly and the interior remains unreacted. However,if an organic material which is chemically unreactive and which does notdissolve the reaction products is added from the initial stage of thereaction, the interior of the reaction system can always maintain afixed temperature distribution by virtue of the vapor of that solvent.As this enables the reaction to take place uniformly and speedily, thereaction time can be shortened. Even if the reaction product becomesfoamed, it is prevented from solidifying by the heat of the vapor of theorganic liquid, so that carbon dioxide generated as a result of thereaction can be discharged into the atmosphere. Accordingly, it ispossible to suppress increase in the volume and to control it. Thus, itis possible to obtain industrially, a soluble resin from tricarboxylicanhydrides and polyisocyanates.

What is called solid state reaction in the present invention is thereaction after tricarboxylic anhydrides and polyisocyanates haveundergone melt reaction, foamed and solidified.

7 DETAILED DESCRIPTION OF THE INVENTION The solid state and melt statereactions The melt state reaction comprises an initial fusing of thetricarboxylic anhydride and diisocyanate at a temperature of below 205C., which temperature varies depending upon the monomer form employed.The melt state reaction is essential to success of the instantinvention, but care must be taken not to exceed 205 C., since gelationand subsequent terpolymerization occurs. Accordingly, must be carriedout at a temperature below The melt state reaction brings gradualincrease to the molecular weight of the polymer in its linear state. Themelt state reaction proceeds at temperatures which eventually exceedthat of the initial tricarboxylic acid anhydride and diisocyanatereaction temperature. Thus, at the point where the melt state reactiontemperature exceeds that of the initial tricarboxylic acid anhydride anddiisocyanate reaction temperature, a solid phase is reached. Theparticular temperature at which the solid state is reached, cannot beexplicitly set forth, since it is obvious that it will vary depending onthe particular monomer employed in the initial reaction. What isimportant, is that the melt state reaction temperature eventuallyexceeds that of the initial reaction temperature between the reactantsemployed, and yet, not exceed the critical limit of 205 C., or fallbelow the lower limit of 40 C. Similarly, no extreme importance isattached to the particular amount of time necessary to achieve the solidphase or solid state point, the main essential feature being theemployment of an initial melt state followed by a solid state reaction.The reaction temperature and time during the melt state, as indicated,will be determined by the particular monomer employed and does not initself, constitute an essential part of the instant invention.

To further define the solid state reaction, this term pertains to thereaction wherein the polymer in its solid phase (see above remarks) isfurther heated to cause an additional increase in the molecular weight,provided however, that the increase in temperature fails to exceed 205C. As to the amount of heat increase necessary to achieve the desiredhigh molecular weight polymer in the solid state, it is sufficient forthe purposes of this invention to say that this will vary depending onthe particular use to which the final product is to be applied.

To reiterate, it is essential to the goals of the present invention that(1) a tricarboxylic acid anhydride/diisocyanate ratio of 1:1 bemaintained, (2) that an initial melt state reaction be employed, and (3)followed by a solid state reaction, the temperature range applicable tothe latter two reactions ranging from 40 C. to 205 C. The failure tooperate within the aforementioned parameters, will lead to a finalproduct of inferior quality and non-applicability to the uses maintainedherein.

The examples of the tricarboxylic anhydrides which may be used in thepresent application are trimellitic anhydride (anhydride of trimelliticacid), hernirnellitic anhydride, etc., which are compounds containing acarboxylic group and an anhydride group. Dicarboxylic acids, which maysubstitute a part of tricarboxylic anhydrides mentioned above within therange permitted by solubility are terephthalic acid,4,4'-dicarboxybiphenol, 4,4-dicarboxyl diphenyl ether, etc., and maycontain in the positions where the alkoxylic group is not substituted agroup such as an alkyl group, alkoxy group, halogen group, haloalkylgroup, nitro group, etc., which does not react with the isocyanategroup, carboxyl group and acid anhydride group. A dicarboxylic acidcontaining a five-memhered imide ring may also be used. Illustrative oftetracarboxylic dianhydrides which may substitute a part of thetricarboxylic anhydrides within the range permitted by solubility are,for example, pyromellitic dianhydride, naphthalene tetracarboxylicdianhydrides, or dianhydrides which have two or more aromatic nuclei ina molecule, e.g., 3.3, 4.4-benzophenone tetracarboxylic dianhydride,biphenyl-3.3', 4.4'-tetracar boxylic dianhydride, etc.

The diisocyanates among the polyisocyanates which may be used in thepresent application are compounds in which two isocyanate groups arepresent as reactive substitutes in the nuclei of benzene, naphthalene,diphenylalkane, diphenylketone, diphenylether, biphenyl, etc. They are,for example, 13-benzenediisocyanate, diphenylmethane-4.4'-diisocyanate,diphenylether-4.4-diisocyanate, 1.5-naphthalenediisocyanate,biphenyl-4.4'-diisocyanate, etc. They may also be diisocyanates whichhave in said nuclei a substitute which does not react with theisocyanate group, carboxylic group and anhydride group, e.g.,2.4-tolylene diisocyanate, 3.6 tolylene diisocyanate, etc., or aliphaticisocyanates containing an aromatic nucleus, e.g., m-xylylenediisocyanate, p-xylylene diisocyanate, etc.

As a suitable solvent, acidic solvents, such as cresols, xylenols, etc.,are most preferable. Solutions may also be made in such basic solventsas N.N-dimethylacetamide, N.N-dimethylformamide, N.N-diethylformamide,N- methyl-Z-pyrrolidone, etc.

It is also possible to use a diluent, a ketonic solvent as acetone,ester solvent as ethyl acetate, or an aromatic hydrocarbon such asbenzene, toluene, xylene, etc. Especially in the case of the solution ofpolymer in cresol, the viscosity of the solution may be greatly reducedby the use of such a diluent.

What is mentioned as solvents which do not react with the isocyanategroup, carboxylic group and acid anhydride group and which do notdissolve the reaction product is a solvent, such as O-dichlorobenzene,which has a halogen bonded to the benzene nucleus, ketonic solvent likeacetone, ester solvent like ethyl acetate, or aromatic hydrocarbons,such as benzene, xylene, toluene, etc., or their mixtures, which aresolvent naphtha having various boiling points. As a solvent naphtha,those having a boiling point of l50200 C., or so are preferable.

In the reaction of the present application, a substance which acts as areaction catalyst for the isocyanate group and active hydrogen may beused. Such a substance markedly accelerates the reaction betweentricarboxylic anhydride and isocyanatcs. For example, the organiccompounds of tin (stannous oleate, dibutyltindilaurate, stannousoct-oate, tributyltin chloride, etc.), tertiary amines (triethylamine,N-ethylm-orpholine or other N-substituted morpholines), alkali metalsalts (lithium ricinoleate, sodium oleate, etc.), heavy metal salts ofcobalt (cobalt naphthenate, cobalt acetate, etc.) and other metal saltsand organic metal compounds are suitable for this purpose. Other organicpolar reagents which may be used as excellent catalysts are, forexample, N,N-dimethylacetamide, N-methyl-Z-pyrrolidone,N,N-diethylformamide, N,N'-dimethylformarnide, hexamethyl-phosphoramide,2,5-dihydrofuran, dimethylsulfone, nitrobenzene, diethyl-cyanamide,acrylonitrile, dimethylthiophene, etc.

In the text of the British patent specification 1,09,956 reference ismade to the manufacture of soluble and fusible resins and an example ofembodiment is given.

A study of this reference is therefore made in References l, 2 and 3 ofthis application. According to the results of the study, as shown inReferences 1 and 2, an unreacted carboxylic group, anhydride group andisocyanate group are still found remaining. Their polymerization degreeis lower than the average polymerization degree 6 (in case carboxylicgroup and anhydride group have completely reacted) and, as is seen fromthe fact that it becomes jelly-like if dissolved inN.N-dimethylacetamide, it is not desirable also from the viewpoint ofstability to prepare the polymer solution with isocyanate group left ina free state.

-As shown in Reference 3, it is seen that the product has nofilm-forming ability and is not good for practical purposes even whenequimolar reaction has been effected.

9 In consequence, if a soluble polymeric product of high molecularweight is to be obtained, it is necessary to carry out solid statepolymerization reaction under fully controlled temperature conditions asdescribed in the present application.

For comparisons sake, references will be given and then embodiments ofthe present invention will be mentioned. These are, however, for thepurpose of aiding in the understanding of the present invention. Thepresent invention is by no means to be restricted by them.

In the references and embodiments mentioned later, the reduced specificviscosity is that measured in N.N-dimethylacetamide at 30 C., at theconcentration of 0.5 gr. polymer in 100 cc. solvent. In preparing thespecimens for this measurement, the reaction products were pulverized ina nitrogen-purged dry box and were put in a flask together with a largequantity of dehydrated and purified methanol and several drops ofN.N-dimethylacetamide; unreacted isocyanate group and anhydride groupreacted, with methanol refluxed in nitrogen gas flow; the disappearanceof absorption by the isocyanate group and anhydride group were confirmedby infrared spectrum, and then the specimen was dissolved in a solventand thrown into a large quantity of methanol, whereby the polymer wasseparated; it was then rinsed and subjected to vacuum drying for 2 daysat room temperature to obtain a powdery resin. The film was obtained byapplying the polymer solution to an aluminum plate, aluminum foil orcopper plate and baking it for 1 hour at 100 C., and another hour at 250C.

The laminated boards were made by impregnating glass fiber material(glass cloth, glass mat, glass robing) or asbestos paper with thepolymer solution, putting such sheets together to the requisitethickness after continuous heating for drying at 80-200 C., and thenpressing them together under the conditions of pressure I-800 kg./cm.temperature 80-400 C., and time -120 minutes.

The N-methyl-Z-pyrrolidone and N.N-dimethyl acetamide used were thosethat had been dehydrated by reflux with an addition of phosphorouspentaoxide after dehydration as an azeotrope with benzene and distilledfor purification. The cresol used was that which had been dehydrated asa benzene azeotrope and then distilled for purification. The methanolused was that which had been dried with an addition of calcium oxide andthen distilled.

The aromatic hydrocarbon used as the heat medium (solvent naphtha) wasthat which had been dehydrated by reflux with an addition of phosphorouspentoxide after dehydration as a benzene azeotrope and then distilledfor purification.

As an apparatus for the reaction, a four-necked flask provided with tworeflux condenser tubes having a calcium chloride tube. in their upperpart and with a thermometer and a stirrer was used. The weighing of allthe specimens was done in a nitrogen-substituted dry box. The reactionwas effected in an oil bath, and all the temperatures shown in thereferences and embodiments are those in the oil bath.

Where a part of tricarboxylic anhydride is substituted with dicarboxylicacid, it is necessary, as shown in the embodiments, that first thetricarboxylic anhydride and diisocyanate are heated for reaction into a.homogenous solution and after continuing the reaction in that state forsome time, the reaction is continued with the addition of a dicarboxylicacid, or that first the dicarboxylic acid and diisocyanate are heatedfor reaction into a homogenous solution and then tricarboxylic anhydrideis added. In the latter case, it takes a considerably longer time thanin the former case to obtain a homogenous solution because thesolubility of dicarboxylic acid in diisocyanate is poor. The reason whyit is necessary to follow the aforementioned procedure is that iftricarboxylic anhydride and dicarboxylic acid and diisocyanate arecaused to react simultaneously, dicarboxylic acid fails to dissolve andfoaming takes place in a heterogeneous state leaving a considerableamount of dicarboxylic undissolved. This is the same wheretetracarboxylic acid dianhydride is used.

The following examples are for the purpose of comparison with theresults of the present invention.

Comparison Example 1 Two reflux condensers provided with calciumchloride tubes in the upper parts, a thermometer and a stirrer wereinstalled in a four-necked flask of 2 liter capacity. 54.89 trimelliticanhydride and 100.0 g. diphenylmethane-4.4'- diisocyanate were weighedout in a nitrogen-substituted dry box to make trimellitic anhydride:diphenylmethane- 4.4'-diisocyanate=1:l.4 (molar ratio). The temperaturewas slowly raised in an oil bath under nitrogen flow, reaction made for1 hour at 125 C., and then temperature slowly raised to 200 C., in 3hours, when, despite strong stirring, the contents foamed and. expandedto fill the flask. In the meantime, the generation of carbon dioxide wasconfirmed by the whitening of an aqueous solution of barium hydroxide.The product obtained is soluble in N.N-dimethylacetamide andN-methyl-Z-pyrrolidone, but in both cases produces a jelly-like filmimmediately after dissolution and foaming is observed; the wholebecoming a jelly-like substance after a while. Specimens of diiferentconcentrations were prepared, but still they became a jelly-likesubstance likewise. It is, on the other hand, insoluble incyclohexanone, ethyl acetate and acetone. Although heated in nitrogenflow for 3 hours at the reflux temperature of each of these solvents, itwas not dissolved. The reduced specific viscosity of the resin obtainedby methanol-treatment of this product was 0.095.

From the infrared spectrum of the reaction product it is noted thatthere remains a series of small absorption bands of 3000-2500 cm? due tocarboxyl group, absorption of 1845 cm.1 due to acid anhydride group andstrongly the absorption of 2260 cm.- due to isocyanate group. In theinfrared spectrum of the reaction product that has been given methanoltreatment, the absorptions of 2260 cm. and 1845 cm. have disappeared.From this fact it has been confirmed that they have completely reactedwith methanol and been blocked.

Comparison Example 2 :In the same way as in Comparison Example 1, g.diphenylmethane-4.4-diisocyanate was molten at 100 C., and 54.8 g.trimellitic anhydride was added and stirring continued.

Temperature was raised to C., and reaction continued for 1 hour, thentemperature raised to C., in another hour, reaction finished and cooled.The product thus obtained is insoluble in ethyl acetate and acetone, anddissolves in cyclohexanone' leaving a part of it undissolved. It issoluble in N.N-dimethylacetamide and N- methyl-Z-pyrrolidone, butbecomes a jelly-like substance just as in the case of ComparisonExample 1. The reduced specific viscosity of the methanol-treatedproduct is 0.051. The findings about its infrared spectrum are the sameas those of Reference 1.

Comparison Example 3 With the same reaction apparatus as in ComparisonExample 1, in use, 48.03 g. (0.25 mol) trimellitic anhydride and 62.56g. (0.25 mol) diphenylmethane-4.4-diisocyanate were weighed out, causedto react for 1 hour at 125 C., in oil bath, then temperature raised toC., in 1 hour 30 minutes, further raised to 200 C., in 1 hour, whenfoaming began to take place in spite of stirring. The reaction was,therefore, brought to an end at this point.

As in the case of References 1 and 2, the infrared spectrum of thereaction product shows that a series of small absorption bands of3000-2500 cm.- due to carboxyl group, absorption of 2260 cm.- due toisocyanate group and absorption of 1845 cm.- due to acid anhydride groupstill intensely remain. The reduced specific viscosity of themethanol-treated resin was 0.088.

The product obtained is soluble in N.N-dimethylacetamide and partlysoluble in cyclohexanone. It is insoluble in ethyl acetate and acetoneeven at their reflux temperatures. Its solution in N.N-dimethylacetamidewas baked on aluminum foil and copper plate. It had no film-form-' ingability but foamed, and cracked upon slight bending.

Comparison Example 4 In the same way as in the case of ComparisonExample 1, 96.06 g. (0.5 mol) of trimellitic anhydride and 125.13 g.(0.5 mol) of diphenylmethane-4.4'-diisocyanate and 10 g. ofN.N-dimethylacetamide are caused'to react, so that trimelliticanhydride:diphenylmethane-4,4-diisocyanate=I:I (molar ratio). They werecaused to react for 1 hour at 120 C., and temperature raised to 160 C.,in 40 minutes, when the product violently foams and solidifies. It ispulverized in nitrogen flow and this porous foamed product is furthersubjected to reaction at 210 C., for 3 hours with slow stirring. Thenthe reaction is brought to an end. If the infrared spectrum of thisproduct is inspected, it is found that the absorption of 2260 cm." dueto isocyanate group still remains. If 20 g. of the reaction product isheated and stirred with an addition of 80 g. of m-cresol, it is stillintransparent. If it is dissolved in N.N-dimethylacetamide, it does notdissolve completely but is in a condition showing a little insolubleturbidity unique to gelation.

Comparison Example 96.06 g. (0.5 mol) of trimellitic anhydride and125.13 g. (0.5 mol) of diphenylmethane 4.4 diisocyanate are caused toreact in 400 g. of m-cresol for 4 hours at 120 C. and for 5 hours at 190C. During that time, there is confirmed a very slow formation of carbondioxide gas, which indicates the proceeding reaction between thetricarboxylic acid and the isocyanate group. The solution thus obtainedbecomes opaque during the reaction and whereby a uniform transparentsolution cannot be given.

EXAMPLES The following examples illustrate the present invention, butare not intended to be limitative of such.

Example 1 Two reflux condensers having calcium chloride tubes in theirupper parts, a thermometer and a stirrer are attached to a four-neckedflask of 2 liter capacity.

96.06 g. (0.5 mol) trimellitic anhydride and 125.13 g. (0.5 mol) ofdiphenylmethane-4.4-diisocyanate and as a catalyst g. ofN-methyl-Z-pyrrolidone were weighed out in a nitrogen-substituted drybox. They were heated for 10 minutes at 120 C. in an oil bath in anitrogensubstituted dry box without stirring until thediphenylmethane-4.4'-diisocyanate was completely dissolved. Stirring wassubsequently commenced. When further heated for one hour at 125 C. withstirring, a great deal of carbon dioxide was generated. Subsequently,the temperature was gradually raised to 195 C. within one hours time,the mixture becoming viscous and producing a foamed product. This wasroughly pulveriezd in nitrogen flow and subjected to solid statereaction for 4 hours. Then the contents of the flask were divided intotwo in two flasks. 400 g. of m-cresol was added to one of them, andheating and stirring were done to stabilize remaining isocyanate groupand to effect dissolution at the same time, when a homogeneoustransparent polymer solution was obtained, 250 g. ofN.N-dimethylacetamide containing 10 g. of rn-cresol was added to theother, and heating and stirring were done to stabilize remainingisocyanate groups and at the same time to effect dissolution. In thiscase, too, a homogeneous transparent polymer solution was obtained. Whenthe infrared spectrum of the reaction product immediately after foamingwas inspected, the absorption of 2260 emsdue to isocyanate was foundstill remaining intensely. In the infrared spectrum of the reactionproduct after solid state reaction Was continued for 4 hours, however,the absorption of 2260 cm.- due to isocyanate group had almostdisappeared. When the infrared spectrum of the polymer solutionstabilized by mcresol was inspected, the absorption of 2260 cm.- due toisocyanate group was found to have completely disappeared. The reducedspecific viscosity of this resin treated with methanol was 0.361.

The film obtained from the solution of polymer dissolved in m-cresol wasa strong, highly flexible and transparent one.

Its tensile strength was 12.8 kg/cmF, elongation 14.7% and electricalproperties: volume resistivity 83x10 Q-cm. at DC 100 v., 23 C.dielectric constant 4.40 in normal condition at 1 kc., 23 C. loss factor84.3 10-* in normal condition at 1 kc., 23 C., and breakdown voltage14.8 kv./0.l mm. (in oil). The properties or enamelled copper wiremanufactured by baking this polymer solution in the usual way are givenin Table 1. The film obtained from the solution of polymer dissolved inN.N-dimethylacetamide was also a strong and highly flexible one.

Example 2 In the same way as in Example 1, 96.06 g. (0.5 mol) oftrimellitic anhydride and 125.13 g. (0.5 mol) ofdiphenylmethane-4.4'-diisocyanate are weighed out. They are caused toreact for one hour at 120 C.125 C. in an oil bath, and subsequently thetemperature is raised to 190 C. within one hour and 30 minutes.Subsequently, the temperature is further raised to 200 C. within onehours time, foaming and solidification taking place. After pulverizingthis product, temperature is raised to 203 C., and reaction continuedfor 5 hours at this temperature.

400 g. of m-cresol is added to one half of the above product at 140 C.,and heated for dissolution, when a homogeneous transparent polymersolution is obtained. 200 g. of N.N-dimethylacetamide (containing 5 g.of mcresol) is added to the other half and heated for dissolution, whena homogeneous transparent polymer solution is obtained. The filmobtained from this polymer solution is a strong, highly flexible andtransparent one. In the infrared spectrum of the solid state reactionproduct before adding 15 g. of m-cresol, the absorption of 2260 cm.- dueto isocyanate group has almost disappeared. The reduced specificviscosity of the methanol-treated resin is 0.302.

Example 3 In the same way as in Example 1, 9600 g. (0.5 mol) oftrimellitic anhydride and 43.54 g. (0.25 mol) of a mixture of2.4-trilenediisocyanate and 2,6 trilenediisocyanate (mixing ratio=8:2)and 62.56 g. (0.25 mol) of diphenylmethane-4.4'-diisocyanate and as acatalyst 10 g. of N.N-dimethylacetamide are weighed out, caused to reactat C., for 2 hours 30 minutes, and the temperature is raised to C., overa period of 1 hour 30 minutes, when foaming and solidifying take place.Then the temperature is raised to C., and solid state reaction continuedfor 4 hours at this temperature. The film obtained from the polymersolution obtained by heating and dissolving it in 500 g. ofN.N-dirnethylacetamide containing 15 g. of m-cresol is a strong, highlyflexible and transparent one. The reduced specific viscosity is 0.341.

Example 4 Two reflux condensers provided with calcium chloride tubes intheir upper parts, a thermometer and a stirrer are attached to afour-necked flask of 2 liter capacity. Into this are weighed out 96.06g. (0.5 mol) of trimellitic anhydride and 125.13 g. (0.5 mol) ofdiphenylmethane- 4.4-diisocyanate and as a catalyst 10 g. of N-methyl-2-pyrrolidone in a nitrogen-substituted dry box. They are heated for 10minutes at 120 C. in oil bath in mtrogen flow without stirring, andstirring is commenced after diphenylmethane-4.4'-diisocyanate has thuscompletely dissolved. If heated for 1 hour at 125 C., a great deal ofcarbon dioxide is generated in the meantime, and when the temperaturehas been raised further to 195 C., over a period of 1 hour, the productbecomes viscous in spite of strong stirring and a porous foamed productis formed. This is roughly pulverized in nitrogen flow, subjected tosolid state reaction for 1 hour, and 100 cc. of solvent naphtha (boilingpoints l92-200 C.) 18 added and the temperature is raised, when refluxbegins to take place after a while. The reaction product is foundseparated from solvent naphtha. After continuing the solid statereaction for about 3 hours, the contents of the reaction vessel aredivided into two flasks. 300 g. of m-cresol is added to one of them, andheating and stirring continued to stabilize the still remainingisocyanate groups and to dissolve the product at the same time, when ahomogeneous transparent polymer solution is obtained. 150 g. ofN.N-dimethylacetamide containing 10 g. of m-cresol is added to theother, and heating and stirring are done to stabilize the stillremaining isocyanate groups and to dissolve the product at the sametime, when also a homogeneous transparent polymer solution is obtained.If the infrared spectrum of the reaction product immediately afterfoaming is inspected, it is found that the absorption of 2260 cm.- dueto isocyanate groups remains intensely. However, in the infraredspectrum of the reaction product after the addition of solvent naphtha,the absorption of 2260 cm." due to isocyanate group has disappeared. Thereduced specific viscosity of this resin treated with methanol is 0.492.

The film obtained from the solution of the polymer in m-cresol is astrong, highly flexible and transparent one. Its tensile strength is13.4 kg./cm. elongation 14.7% and electrical properties as follows:insulation resistance 8.9 10 n-cm. at DC 100 v. 23" C., dielectricconstant 4.36 in normal condition at 1 kc., 23 C., loss factor 90.4 10-in normal condition at 1 kc., 23 C., and insulation breakdown voltage14.5 kv./0.l mm. (in oil). The properties of enamelled copper wiremanufactured by baking this polymer solution in the usual way are shownin Table 1. The film obtained from the solution of the polymer inN.N-dimethylacetamide was also found to be strong, highly flexible one.

Example 5 In the same way as in Example 1, 96.06 g. (0.5 mol) oftrimellitic anhydride and 125.13 g. (0.5 mol) ofdiphenylmethane-4.4'-diisocyanate and as a catalyst g. ofN.N-dimethylacetamide were weighed out and caused to react at 120 C. for1 hour, when a great deal of carbon dioxide is generated. At thistemperature a great deal of carbon dioxide is generated, while inExample 3 very little carbon dioxide is generated at this temperature.When the carbon dioxide generated was collected in water, it was morethan three times that produced in Example 3. The temperature was furtherraised to 160 C., over a period of 30 minutes, when the product foamsviolently and solidifies. After pulverizing it in nitrogen flow, thetemperature is raised to 190 C., and 200 cc. of solvent naphtha (boilingpoint 165 C.175 C.) is added, when reflux begins after a while. Reactionis continued at this temperature for 3 hours, 10 g. of m-cresol is thenadded and the reaction is completed in 30 minutes. If the polymerobtained is heated and dissolved in m-cresol, it produces a homogeneousand transparent polymer solution. It is also soluble inN-methyl-2-pyrrolidone, N.N-dimethylacetamide and N.N-dimethylformamide.The film obtained from the solution of the polymer in N-methyl-2-pyrrolidone was found to be a strong, highly flexible and transparentone. Its tensile strength was 12.7 kg./cm. and elongation 13.9%. Whenthis film has been immersed in a 5% aqueous solution of caustic soda for24 hours, no change in it was observed. The reduced viscosity of theresin treated with methanol was 0.450. The coating film baked on acopper plate did not crack when wound around a rod of a 3 mm. diameter.

Example 6 In the same way as in Example 1, 96.06 g. (0.5 mol) oftrimellitic anhydride and 125.13 g. (0.5 mol) ofdiphenylmethane-4.4'-diisocyanate are weighed out. Reaction made for 1hour at C. C. in oil bath, and the temperature is further raised to 180C., when foaming and solidifying take place. After this product ispulverized, 100 g. of solvent naphtha (boiling point 190 C.-195 C.) isadded and the temperature is raised to 203 C., when the reflux ofsolvent naphtha begins after a while. Reaction continued at thistemperature for 3 hours, then 15 g. of m-cresol is added and thereaction was carried out for 30 minutes to complete it. If 350 g. ofm-cresol is added to one half of this (containing solvent naphtha) at C.and heated for dissolution, a

homogeneous and transparent polymer solution is obtained. If 200 g. ofN.N-dimethylacetarnide (containing 5 g. of m-cresol) is added to theother half and heated for dissolution, a homogeneous and transparentpolymer solution is obtained. The film obtained from this polymersolution is a strong, highly flexible and transparent one. If theinfrared spectrum of the reaction product before the addition of 15 g.of m-cresol is inspected, it is found that the absorption of 2260 cm?due to isocyanate group has almost disappeared.

The reduced specific viscosity of the resin treated with methanol is0.320.

Example 7 In the same way as in Example 1, 96.06 g. (0.5 mol) oftrimellitic anhydride and 43.54 g. (0.25 mol) of a mixture of2.4-trilenediisocyanate and 2.6-trilenediisocyanate (mixing ratio 8:2)and 62.56 g. (0.25 mol) of diphenylmethane-4.4'-diisocyanate and as acatalyst 10 g. of N.N- dimethylacetamide are weighed out. They arecaused to react at 11-0 C. for 2 hours 30 minutes and the temperture israised to C., over a period of 1 hour, when foaming and solidifying takeplace. If 150 cc. of solvent naphtha (boiling point C. C.) is added thenreflux begins after a while, and solid state reaction is continued atthis temperature for 3 hours. The film obtained from the polymersolution obtained by heating and dissolving this product in 450 g. ofN.N-dimethylacetamide is a strong, highly flexible and transparent one.The reduced specific viscosity is 0.371.

Example 8 In the same way as in Example 1, 96.06 g. (0.5 mol) oftrimellitic anhydride and 125.13 g. (0.5 mol) of diphenylmethane-4.4diisocyanate and as a catalyst 10 g. ofN-methyl-Z-pyrrolidone are weighed out, caused to react for 1 hour at120 C., and the temperature is raised to 200 C., over a period of 1hour, when foaming and solidifying take place. After roughly pulverizingin nitrogen fiow, 500 cc. of solvent naphtha (whole boiling point is 165C.175 C. and which has previously been heated in another flask to thereflux temperature) is added and refluxed, then 10 g. of m-cresol isadded and the reaction completed in 30 minutes. 400 g. of m-cresol isadded to one half of the polymer obtained by removing the solventnaphtha, and heated for dissolution, when a homogeneous and transparentpolymer solution is obtained. 230

15 g. of N-methyl-Z-pyrrolidone (containing g. m-cresol) is added to theother half, and heated for dissolution, when also a homogeneous andtransparent polymer solution is obtained. The reduced specific viscosityis 0.377. If the infrared spectrum of the reaction product immediatelyafter foaming is inspected, it is found that the absorption of 2260 cm.due to isocyanate group is almost disappeared in the infrared spectrumof the reaction product after the addition of solvent naphtha. The filmsobtained from the solutions of the polymer is m-cresol andN-methyl-Z-pyrrolidone were found to be strong, highly flexible andtransparent ones.

Example 9 In the same way as in Example 1, 12.46 g. (0.075) ofisophthalic acid and 62.56 g. (0.25 mol) ofdiphenylmethane-4.4'-diisocyanate and as a catalyst 7 g. of N-rnethyl-Z-pyrrolidone are weighed out and caused to react at 130 C. for45 minutes, when isophthalic acid at last begins to dissolve into ahomogeneous condition, when the solution is light grey and transparent.After a lapse of further 20 minutes, it becomes yellow. At this point,33.62 g. (0.175 mol) of trimellitic anhydride is added and reactioncontinued for 45 minutes, and then the temperature is raised to 180 C.,in 1 hour, when the product foams and solidifies. If 200 cc. of solventnaphtha (boiling point 165 C-175 C.) is added, reflux begins after awhile. After reaction at this temperature for 3 hours, 150 cc. ofsolvent naphtha is removed and 250 g. of N.N-dimethylacetamide(containing 4 g. of mcresol) is added to dissolve it to obtain a polymersolution while stabilizing the still remaining isocyanate groups withm-cresol. The reduced specific viscosity of the methanol-treated resinwas found to be 0.354.

The properties of enamelled copper wire manufactured by baking thispolymer solution in the usual way as shown in Table 1.

Example Two reflux condensers provided the calcium chloride tubes intheir upper parts, a thermometer and a stirrer are attached to afour-necked flask of 2 liter capacity. 96.06 g. (0.05 mol) oftrimellitic anhydride and 125.13 g. (0.5 mol) ofdiphenylmethane-4.4'-diisocyanate and as a catalyst, 5 g. ofN-methyl-Z-pyrrolidone and cc. of solvent naphtha (boiling point 192-200C.) are weighed out in a nitrogen-substituted dry box. They are heatedfor 10 minutes at 120 C. in oil bath without stirring in nitrogen flow,and stirring is begun after diphenylmethane-4.4'-diisocyanate hascompletely dissolved. If heated for 1 hour at 125 C., a great deal ofcarbon dioxide is generated in the meantime, and when the temperature israised to 195 C., in 1 hour, the product becomes viscous in spite ofstrong stirring and a porous foamed product is formed. The volume of theproduct in the reaction vessel was found to be about of the capacity ofthe vessel. After 1 hour, the product is roughly pulverized in nitrogenflow, kept at 220 C., with an addition of 20 cc. solvent naphtha(boiling point 192- 200 C.) and subjected to solid state reaction for 1hour 30 minutes. The reaction product is found separated from solventnaphtha. The contents of the reaction vessel are divided into twoflasks. 300 g. of m-cresol is added to one of them, and heated furtherand stirred for stabilizing the still remaining isocyanate groups andfor dissolving at the same time, when a homogeneous transparent polymersolution is obtained. 250 g. of N.N-dimethylacetamide containing 10 g.of m-cresol is added to the other half and heated and stirred fordissolving, when also a homogeneous transparent solution is obtained. Ifthe infrared spectrum of the reaction product immediately after foamingis inspected, it is found that the absorption of 2260 cm? due toisocyanate group remains intensely. However, in the infrared spectrum ofthe reaction product after the addition of solvent naphtha, theabsorption of 2260 em.- due to'isocyanate group has disappeared. Thereduced specific viscosity of this resin treated with methanol is 0.570.

The film obtained from the solution of this resin dissolved in m-cresolis a strong, highly flexible and transparent one. Its tensile strengthis 13.4 kg./mm. and elongation 14.7%. Its electrical properties are asfollows: insulation resistance 8.9 10 Q-cm. at DC v., 23 C.; dielectricconstant 4.36 in normal condition at 1 kc., 23 C.; loss factor 90.4X10-in normal condition at 1 kc., 23 C.; and insulation breakdown voltage14.5 kv./ 0.1 mm. (in oil). The properties of enamelled copper wiremanufactured by baking this polymer solution in the usual way are shownin Table 1. The film obtained from a solution of the polymer dissolvedin N.N-di methylacetamide was also found to be a strong and highlyflexible one.

Example 11 In the same way as in Example 1, 96.06 g. (0.5 mol) oftrimellitic anhydride and 125.13 g. (0.5 mol) ofdiphenylmethane-4.4'-diisocyanate and 50 cc. of solvent naphtha (boilingpoint 192-200 C.) were measured out into the reaction vessel, caused toreact for 1 hour at C., and then the temperature raised to 200 C., in 1hour, when foaming and solidifying took place. The volume of thereaction product in the reaction vessel was found to be about A of thecapacity of the vessel.

A solid state reaction is made at this temperature for 3 hours. 350 g.of m-cresol were added to one half of the polymer and heated fordissolving, thus obtaining a homogeneous and transparent polymersolution. 220 g. of N-methyl-2-pyrro1idone (containing 5 g. of m-cresol)was added to the other half, and heated for dissolving, when also ahomogeneous and transparent polymer solution was obtained. The reducedspecific viscosity is 0.405. If the infrared spectrum of the reactionproduct immediately after foaming is inspected, it is found that theabsorption of 2260 cm." due to isocyanate group remains intensely. Inthe infrared spectrum of the reaction product of the solid statereaction, however, the absorption of 2260 cm.- due to isocyanate grouphas already disappeared. The films obtained from the solutions of thepolymer dissolved in 'm-cresol and in Nmethyl-2-pyrrolidone were foundto be strong, highly flexible and transparent ones.

Example 12 In the same way as in Example 1, 96.06 g. (0.5 mol) oftrimellitic anhydride and 87.03 g. (0.5 mol) of a mixture of2.4trilenediisocyanate and 2.6-trilenediisocyanate (mixing ratio 8:2)and 0.2 g. of a mixture in equal mols of dibutyltin dilaurate andtriethylamine and 20 cc. of solvent naphtha (boiling point -175" C.) aremeasured out, caused to react for 2 hours at 110 C., and the temperatureis raised to C., in 1 hour, when foaming and solidifying take place.After 1 hour, 20 cc. of solvent naphtha (boiling point 165l75 C.) isadded and solid state reaction continued for 2 hours at 200 C. Thevolume of the reaction product in the reaction vessel was found to beabout /2 of the capacity of the vessel. The film obtained from thepolymer solution prepared by heating and dissolving this in 400 g. ofN.N-dimethyl acetamide containing 15 g. of m-cresol is strong, highlyflexible and transparent. The reduced Specific viscosity is 0.393.

TABLE 1 Example 1 Example 4 Example 9 Example 10 Construction:

Conductor diameter (mm) 1.003. 1.003- 1.004. 1.003. Finished diameter(mm.). 1.063. 1.063- 1.084. 1.079. Film thickness (mm.) 0.030- 0.030-0.040- 0.040.

Flexibility:

Jerking- Good Goo Good. Good. Winding pinholes. dn do 1d good. 1d good.Heat-shock:

Normal winding:

250 C.X2 hr 2d good- 2d good 2d good 2d good 300 C.X2 hr ..do ..do

Cut through temperature: 4-point cross load 5 kg., 365 C. or more- 365C. or more- Good- Resistance to Styrol: 120 0 Resistance to chemicals:

Immersion 50 C.X2 hr.:

N.N-dimethyl-acetamige -do -do o Do. 350 C. or more 365 C. or more.

Goo Good. D

0 Resistance to abrasion: 700 g. load, round-trip 143..."

number.

Although the present invention has been adequately described in theforegoing specification and examples included therein, it is readilyapparent that various changes and modifications can be made withoutdeparting from the spirit and scope thereof.

What is claimed is:

1. A method for preparing phenolic acidic solventsoluble and infusiblelinear aromatic polyamide-imides of high molecular weight, the molecularstructure of which includes amide bonding and a S-membered imide ringwhich comprises subjecting a tricarboxylic anhydride and a diisocyanateto heating and melt state reactions at a temperature of from about 40 C.to not exceeding 205 C., and then subjecting said reactants to a solidstate polymerization reaction at a temperature of from about 40 C. tonot exceeding 205 C., the molar ratio of said diisocyanate to saidtricarboxylic anhydride being 1:1, said melt state reaction beingcarried out for an amount of time sufiicient to bring a gradual increaseto the molecular weight of the polymer in its linear state and to causethe melt state reaction temperature to exceed the initial tricarboxylicacid anhydride and diisocyanate reaction temperature and, said solidstate reaction being carried out for an amount of time sufficient topermit the polymer, in its solid phase, to increase in molecular weight.

2. The method of claim 1, wherein a chemically inert liquid, notreactive with isocyanate, carboxyl or acid anhydride groups and whichwill not dissolve the reaction product, is used as a heating medium insaid solid state polymerization as a means for obtaining a uniformdistribution of reaction temperature not exceeding 205 C.

3. The method of claim 2, wherein said chemically inert liquid is addedfrom the initial period of the melt state reaction.

4. The method of claim 1, wherein a material selected from the groupconsisting of an organic polar reagent and an organic metallic compound,to promote the reaction of isocyanate groups and active hydrogen, isemployed as a catalyst to accelerate the reaction.

5. The method of claim 2, wherein an aromatic hydrocarbon is employed asthe chemically inert liquid.

6. The method of claim 3, wherein an aromatic hydrocarbon is used as thechemically inert liquid.

References Cited UNITED STATES PATENTS 3,314,923 4/1967 Muller et al26077.5 M 3,347,828 10/1967 Stephens et al. 26047 CP 3,445,477 5/1969Muller et al. 26030.2 3,489,696 1/1970 Miller 26078 TF 3,518,230 6/1970Sheifer et al. 26033.4 P 3,578,639 5/1971 Sheffer 26033.4 P

ALLAN LIEBERMAN, Primary Examiner US. Cl. X.R.

